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A month after a mass shooting left 17 dead at Marjory Stoneman Douglas High School in Parkland, Fla., thousands crowded into downtown Washington for a protest dubbed the March for Our Lives. Bearing signs and chanting, demonstrators — led by survivors of the Stoneman Douglas massacre — called for action by Congress on gun control in response to the nation’s relentless two-decade stretch of campus shootings. Hundreds of “sibling marches” took place in cities across the United States.

Hundreds of thousands of demonstrators crowd downtown Washington on Saturday for the March for Our Lives rally to call for stricter gun-control measures. Salwan Georges/The Washington Post

Hunter Nguyen, 21, of Hagerstown, Md., left, and Daisy Hernandez, 22, of Stafford, Va., hold up their palms, featuring the message “Don't Shoot,” as they participate in the march. Matt McClain/The Washington Post

Marjory Stoneman Douglas High School student Allison Laveaux gathers with others near the rally stage. Many Stoneman Douglas students were in attendance. Matt McClain/The Washington Post

Thousands packed the streets of Washington for the rally, calling on members of Congress to pass new gun-control laws. Salwan Georges/The Washington Post

Eva Plank, 19, of Baltimore, fashions a sign before the start of the rally. The march was bankrolled by celebrities, but non-famous young people have been the face of the movement. Salwan Georges/The Washington Post

District resident Muna Said, 14, rests her head on the shoulder of her sister, 16-year-old sister Munira, before the start of the March for Our Lives rally. Matt McClain/The Washington Post